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NASA Comet Hunter Closing on Quarry

Having trekked 3.2 billion kilometers (2 billion miles) across cold, radiation-charged and interstellar-dust-swept space in just under five years, NASA's Stardust spacecraft is closing in on the main target of its mission -- a comet flyby.

"As the saying goes, 'We are good to go,'" said project manager Tom Duxbury at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "There are significant milestones ahead that we need to achieve before we reach the comet on Jan. 2, but we have a great team of engineers and scientists that have trained hard for this moment, and we have a spacecraft that is in great shape."

All this intense earthly preparation is directed at Wild 2 (pronounced Vilt 2), a ball of dirty ice and rock, about as big as 20 Titanics laid end-to-end. Discovered in 1978, Wild 2 orbits the Sun once every 6.39 years on a trajectory that carries it nearly as close to the Sun as Mars is, and as far away from the Sun as Jupiter.

On Jan. 2 at 11:40:35 am PST, the 5.4-kilometer-wide (3.3- mile) comet will sail past the 5-meter-long (16-foot) Stardust spacecraft at a distance of about 300 kilometers (186 miles) and at a relative speed of 21,960 kilometers per hour (13,650 miles per hour). The plan is thus because Stardust is a sample return mission.

"In recent decades, spacecraft have passed fairly close to comets and provided us with excellent data," said Dr. Don Brownlee of the University of Washington, principal investigator for the Stardust mission. "Stardust, however, marks the first time that we have ever collected samples from a comet and brought them back to Earth for study."

Clad for battle behind specially designed armored shielding, Stardust will document its passage through the hailstorm of comet debris with two scientific instruments that will scrutinize the size, number and composition of dust particles in the coma – the region of dust and gas surrounding the comet's nucleus. Along with these instruments, the spacecraft's optical navigation camera will be active during the flyby and should provide images of the dark mass of the comet's nucleus. Data from all three will be recorded onboard Stardust and beamed back to Earth soon after the encounter.

The chain of events began nine days out from the comet when Stardust deployed its "cometary catcher's mitt," a tennis- racket-shaped particle catcher of more than 1,000 square centimeters (160 square inches) of collection area filled with a material called aerogel. Made of pure silicon dioxide, like sand and glass, aerogel is a thousand times less dense than glass because it is 99.8 percent air. The high-tech material has enough "give" in it to slow and stop particles without altering them radically.

"The samples we will collect are extremely small, 10 to 300 microns in diameter, and can only be adequately studied in laboratories with sophisticated analytical instruments," said Brownlee. "Even if a ton of sample were returned, the main information in the solids would still be recorded at the micron level, and the analyses would still be done a single grain at a time."

After the sample has been collected, the collector will fold down into a return capsule, which will close like a clamshell to secure the sample for a soft landing at the U.S. Air Force's Utah Test and Training Range in January 2006. The capsule, holding microscopic particles of comet and interstellar dust, will be taken to the planetary material curatorial facility at NASA's Johnson Space Center, Houston, Texas, where the samples will be carefully stored and examined.

Scientists believe in-depth terrestrial analysis of cometary samples will reveal a great deal not only about comets but also related to the earliest history of the solar system. Locked within the cometary particles is unique chemical and physical information that could provide a record of the formation of the planets and the materials from which they were made.

Stardust, a project under NASA's Discovery Program of low- cost, highly focused science missions, was built by Lockheed Martin Space Systems, Denver, and is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena.